Teste si le login existe dans l'annuaire LDAP !

src/UnicaenOauth/OAuth2/Adapter/StorageAdapter.php

@@ -40,9 +40,11 @@ class StorageAdapter extends PdoAdapter
             return parent::checkPassword($user, $password);
         }
 
-        $user = $this->getUser($username);
+        if ($user = $this->getUser($username)) {
+            return $this->checkPassword($user, $password);
+        }
 
-        return $this->checkPassword($user, $password);
+        return false;
     }
 
     /**